diff --git a/browser/base/content/browser.js b/browser/base/content/browser.js
index bbfef0049b..a8aff1bd7b 100644
--- a/browser/base/content/browser.js
+++ b/browser/base/content/browser.js
@@ -8144,12 +8144,12 @@ var ToolbarIconColor = {
     let luminances = new Map;
     for (let toolbar of document.querySelectorAll(toolbarSelector)) {
       let [r, g, b] = parseRGB(getComputedStyle(toolbar).color);
-      let luminance = 0.2125 * r + 0.7154 * g + 0.0721 * b;
+      let luminance = (2 * r + 5 * g + b) / 8;
       luminances.set(toolbar, luminance);
     }
 
     for (let [toolbar, luminance] of luminances) {
-      if (luminance <= 110)
+      if (luminance <= 128)
         toolbar.removeAttribute("brighttext");
       else
         toolbar.setAttribute("brighttext", "true");